US Patent 7295140 Oversampling analog-to-digital converter and method with reduced chopping residue noise

A delta-sigma modulator includes a chopper-stabilized integrator, a quantizer having an input coupled to an output of the integrator, an input signal acquiring circuit controlled by a switched reference feedback circuit and having an output coupled to the input of the integrator, and a frequency-shaped pseudo-random chopper clock signal generator circuit including a pseudo-random sequence generator and producing a frequency-shaped pseudo-random clock signal. Resetting circuitry is coupled to reset inputs of the pseudorandom sequence generator to reset it in synchronization with the digital output of the chopper-stabilized delta-sigma modulator to prevent noise caused by wrap-around operation of the pseudorandom sequence generator. A logic circuit produces chopper clock signals in response to the frequency-shaped pseudo-random clock signal and applies them to various input switches and output switches of the integrator.